In the related art, there is a decolorizing apparatus which erases an image by heating a sheet having the image formed with a decolorable colorant at a decolorable temperature. It is possible to erase the image formed on the sheet using the decolorizing apparatus, thereby allowing the sheet to be reused.
If the same sheet is used many times, some images are not completely erased and remain, and thus visibility is deteriorated. Accordingly, some decolorizing apparatuses print a mark indicating the number of times of erasing on a margin of a sheet each time an image is erased, and if there are marks of a predetermined number or more, the apparatuses treat the sheet as a non-reusable sheet and transport the sheet to a predetermined tray.